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August 16, 2016, 10:05 |
CFX Warning Error
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#1 |
Member
Chaitanya
Join Date: Mar 2016
Location: Stuttgart, Germany
Posts: 50
Rep Power: 10 |
Hi,
I am running a CHT transient Simulation and trying to model the Radiation losses. I include the Monte carlo Radiation model for modeling the Radiation losses. I get a warning: In Analysis 'Flow Analysis 1' - Domain Interface 'Default Fluid Solid Interface': At least one domain coupled to this interface is either a solid domain with radiation or has a laminar fluid flow with radiation. When such a domain is coupled by an interface with a Heat Transfer Interface Model, accuracy issues can arise with calculating the temperature of the wall. What does it mean with accuracy issues. ? I fail to understand. The Radiation model is for the solid Domain. I have a laminar flow. I include Radiation model aas below: radiation_model.PNG. |
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August 17, 2016, 08:22 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
Rep Power: 143 |
Please do not post multiple identical posts. If people are not answering your post think about why not - and improve your question. Do not just post the same thing all over again. I have removed the duplicate post.
Your problem is from something in how you set up your model. I cannot tell what from the simple information you have posted. But before you consider that - do you really need the Monte Carlo radiation model? Would the Discrete Transfer model be adequate? In fact, would a heat sink on the surface of the body with the simple radiation heat transfer equation be enough? Then you don't need to model radiation at all. |
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August 17, 2016, 08:35 |
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#3 |
Member
Chaitanya
Join Date: Mar 2016
Location: Stuttgart, Germany
Posts: 50
Rep Power: 10 |
Sorry for duplication. I got a message yesterday, that I posted in the wrong Forum and my post is deleted. So I reposted.
I would be careful next time about this. Thanks for notifying this. 1. I want to model Radiation of a solid surface which is at a consireably high temp. (600K). See how it cools with time. In solids I only have a Monte carlo Option for Radiation modeling. The only other way I could think is using a CEL to model q = σ T4 -T04 A. |
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August 17, 2016, 20:10 |
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#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
Rep Power: 143 |
Does the radiatitive heat pass through the solid? In other words, is the solid transparent (or at least partially transparent)? I am not referring to the conducted heat here, just the radiation.
Or does it just pass through the air and heat the surface of the solid? |
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August 18, 2016, 03:12 |
Cht
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#5 |
Member
Chaitanya
Join Date: Mar 2016
Location: Stuttgart, Germany
Posts: 50
Rep Power: 10 |
Ahhhhh... Now I get your point. Your question answers my question. !!
I am stupid. My material is silicon carbide which is opaque. So I would probably not need a radiation model for the solid. I will check with the emissivity coefficient for silicon carbide. For a radiative model heat loss in a fluid model, I think the losses are high since the temp is high in the range of 600K. So I would use a discrete transfer model for heat losses for this model and check the model how it works. I guess analytical calculations also work. |
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August 18, 2016, 03:20 |
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#6 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
Rep Power: 143 |
The analytical calc will work fine providing surfaces do not irradiate other surfaces significantly. In the flutes of the drill (I assume it is a drill) this probably will happen so that means you will need the discrete transfer model.
Either way, this is a zillion times easier than with the Monte Carlo model. |
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August 18, 2016, 03:43 |
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#7 |
Member
Chaitanya
Join Date: Mar 2016
Location: Stuttgart, Germany
Posts: 50
Rep Power: 10 |
Perfect analysis!!
For my case, the flutes of the drill are not at conisderably high temperatures. I guess I can neglect radation losses in this region. Only the cutting edge of the drill is at a high temperature. Thus it would be a good idea to analytically evaluate. or use discrete transfer model. The problem is I cannot include radiative losses without creating a fluid domain of the surrounding air where it loses heat. I can model convective losses to the surrounding air by HTc BC. So I guess, Using a CEL expression to combine this convective and radiative losses will make more sense unless you know of some other way. ! |
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August 18, 2016, 07:08 |
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#8 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,703
Rep Power: 143 |
A CEl expression to combine convection and radiation is easy and works fine. If this is an appropriate boundary condition then I would use it.
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